The objectives of this study are to extend our understanding of gonadotropin releasing hormone (GnRH) containing neurons in both neuroendocrine and neuroregulatory pathways, by characterizing their intercellular contacts, their dendritic aborization, and identifying some afferent connections involved in their control. Immunocytochemical (ICC) staining for GnRH in the baboon brain has revealed numerous apparent synaptic contacts between GnRH containing elements at the light microscopic (LM) level. Stained, plastic embedded tissue sections are examined by electron microscopy (EM) to determine the nature of these junctions. Thicker sections of the hypothalamus and forebrain are also stained for immunoreactive GnRH neurons using o-dianisidine as the substrate. They are then treated with the rapid Golgi technique, a method compatable with the ICC reaction product. Silver impregnation provides detailed morphology of identified GnRH neurons or of the afferent and efferent connections of these cells. Interactions between GnRH neurons and dopaminergic afferents are identified by double staining with antibodies to GnRH and tyrosine hydroxylase using diaminobenzidine and o-dianisidine as separate substrates. Likewise, interactions between GnRH and enkephalin containing cells and processes are recognized by using antibodies to these two peptides and separate substrates. Contacts observed at the LM level are examined by EM. Direct evidence for dopaminergic (DA) control of GnRH secretion in the median eminence (ME) is also sought. ME synaptosomes are stained for DA receptor sites by the preembedding ICC technique developed in my laboratory, using haloperidol, and antiserum against haloperidol, and the PAP technique. Pellets of labeled ME synaptosomes are thin sectioned and stained for GnRH using post-embedding ICC, to show the DA receptor sites exist on GnRH nerve terminals. This information regarding GnRH neuronal morphology, interconnections, afferents, efferents, and control will enhance our knowledge of neural control of reproduction and sexual behavior.